Gas turbine and method for varying the aerodynamic shape of a gas turbine blade

ABSTRACT

A gas turbine and a method for varying the aerodynamic shape of a blade of the gas turbine is disclosed. The blade has a coating made of a shape-memory alloy. Hot air is transported via channels to the coated blade in order to cause a phase change in the coating and an aerodynamic shape change to the blade.

BACKGROUND AND SUMMARY OF THE INVENTION

This application claims the priority of International Application No. PCT/DE2009/000997, filed Jul. 17, 2009, and German Patent Document No. 10 2008 033 783.8, filed Jul. 18, 2008, the disclosures of which are expressly incorporated by reference herein.

The invention relates to a gas turbine having guide blades and rotor blades in the compressor section and turbine section.

Gas turbines are used as aircraft propulsion devices in particular and have at least one rotor and at least one stator, and namely both in the compressor region as well as in the turbine region. The rotor blades assigned to the rotor rotate vis-à-vis the stationary housing and the likewise stationary guide blades.

Gas turbines, particularly aircraft gas turbines, are subject to different ambient conditions and flow conditions, which they undergo during operation. Because of these different conditions, it is desirable to temporarily vary the geometric shape of the blades. Various forms of so-called adaptive blades have already been envisaged. One of these options consists of wires made of shape-memory alloys being used on or in a blade to change the shape of the profile. These wires are heated electrically until the abrupt phase change specific to shape-memory alloys occurs. Because of the resulting changing shape of the wires (expansion or contraction), the blade shape is modified.

However, this method for varying the aerodynamic shape of a blade is associated with very high electrical energy expenditures, because the required amounts of energy (particularly the current strengths) must be very great and naturally must be made available externally. In addition, the wires also have to be insulated from one another, in other words, in order to reduce expenditures, until now these wires have been used only with non-metallic blades or sections thereof.

The object of the invention is making a gas turbine available in which the aerodynamic shape change of the blades may take place in a simplified manner. In addition, it is also an object to disclose a method for varying the aerodynamic shape of a blade of a gas turbine during its operation that can be realized in the most cost-effective manner possible.

The gas turbine according to the invention has guide blades and rotor blades in the compressor section and turbine section. At least some of the blades have a coating of a shape-memory alloy. At least one channel that optionally directs hot air ends in such a way at one or more coated blades that the hot air causes a phase change of the alloy such that the blade varies its aerodynamic shape.

In the case of the gas turbine according to the invention, the shape-memory material is applied to a blade by alloying in such a way that a simple and optimal connection is produced between the blade and its coating. Activation of the shape-memory material is not brought about electrically, but via the customary hot air that is available anyway in the case of gas turbines, which is transported to the shape-memory material via at least one hot air channel. The amount of energy transported by the hot air must be sufficient to cause the phase change. Naturally, a specific quantity of hot air could be directed continuously to the coated blade and then an additional amount of hot air energy could be transported there just for the phase change. As an alternative to this, hot air is directed to the coated blade or coated blades only when the phase change is supposed to be brought about. A further advantage of the invention is that blowing in air, particularly in the case of a compressor, makes it possible to prevent so-called pumping, which may occur preferably in the partial load range (off-design state). Feeding the hot air also thereby optionally fulfills a dual function, namely improved compressor stabilization along with the blade shape change. In addition, because no electrical energy is required for the phase change, the coated blades may be made of metal.

The blades are preferably coated on the outer side with the shape-memory alloy. Naturally, as an option, the blade could also be coated on the inside, namely in that they are designed to be hollow on the inside.

According to the preferred embodiment, the coated blades are compressor blades, with which naturally the temperature is not as high as in the turbine region, whereby great temperature differences may be generated between the hot air feed and the hot air interrupt.

The channel or channels start in particular from a downstream compressor stage and direct hot air upstream from this compressor stage.

The channel or the channels may end at the housing and from there guide the hot air in the direction of the blades and/or discharge into the interior of the coated blade and blow hot air into the blade. This hot air can then be directed for example via openings to the outer side of the blade, where the coating of the shape-memory alloy is heated abruptly.

According to one embodiment, the coated blades are guide blades and/or rotor blades.

Because of the invention, it is also possible to provide a gas turbine which functions without a variable guide baffle.

In addition, according to the invention it is provided that the blade, which is coated with the shape-memory alloy, is made of metal.

The inventive method for varying the aerodynamic shape of a blade of a gas turbine is characterized by the following steps:

a) Providing a coating of a shape-memory alloy on the blade, and

b) Optionally conveying hot air to cause the phase change in the coating.

According to the preferred embodiment, hot compressor air is used as the hot air.

Additional features and advantages of the invention are yielded from the following description and from the following drawings to which reference is made.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal section through a gas turbine according to the invention, and

FIG. 2 is a schematic longitudinal section through the compressor region of the gas turbine according to FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a gas turbine having an inlet diffuser 10, a compressor 12, a combustion chamber 14, a turbine 16 and a thrust nozzle 18, all of which are situated in a housing 20. Only by way of example, several of the numerous rotor blades 22 are depicted as part of the rotor and guide blades 24 are depicted as part of the stator in the compressor section or turbine section.

FIG. 2 shows that the depicted compressor 12 is multi-stage and has an axial design. It is easy to see that the guide blades 24 are connected to the housing 20 and the rotor blades 22 are connected to the rotor 26.

Directly upstream from the so-called blade tip 28 of a rotor blade ring, the housing 20 has several uniformly distributed blow-in openings 30 for hot gas on the circumference. The blow-in openings 30 are the end of one or more channels 32, which direct hot air upstream from a downstream compressor stage via one or more outlet openings 34. Arrow 36 symbolizes the hot gases.

Alternatively or additionally, the channels 32 may also discharge into hollow blades 22 or 24. Corresponding cavities in the interior of a guide blade 24 are identified by the reference number 38 and are depicted by broken lines.

Optionally, shut-off devices 40 may also be arranged in the channels 36, which release or interrupt the hot gas flow. The location of these shut-off devices 40 is not restricted to the position indicated in FIG. 2.

Some or all of the guide blades and rotor blades 22, 24 of one or more stages are provided at least in sections with a coating 42 on the outer side.

This coating 42 is provided preferably in the region of the side of the corresponding blades 22, 24 that faces upstream.

The shape-memory alloys are designated as memory-alloy components or memory-alloy materials. These types of material change their structural phases when exceeding or falling short of characteristic temperature values.

Possible materials are nickel-titanium alloys, copper-zinc-aluminum alloys or copper-aluminum-nickel alloys for example. Naturally, this enumeration is not conclusive.

The coating 42 is applied during the manufacture of the blades 22, 24 in such a way that no prefabricated part made of a shape-memory alloy must be attached separately. The material of which the blades 22, 24 are made is preferably a metal alloy.

Due to the following properties, the depicted gas turbine does not have a variable guide baffle, a fact that simplifies the gas turbine in terms of its structure and manufacture.

The outer-side coating 42 of a shape-memory alloy may optionally undergo a phase change when the gas turbine is in operation, which is achieved by targeted heating by means of the hot air 36. Starting with a specific operating state, it may be desirable to vary the aerodynamic shape of individual blades 22 or 24. To do so, hot air is conveyed from downstream compressor stages via the channel or channels 32 to upstream compressor stages, either via the housing 20 and corresponding inlet openings 30, or via the hollow interior of blades 22, 24, whose cavities 38 preferably end on the outer side (particularly on the upstream outer side) of the corresponding blade 22, 24. The hot air encountering the coating 42 produces a phase change so that the thin alloy layer contracts or expands. Because the layer is applied to the entire surface of the blade 22, 24, the blade 22, 24 is bent in the desired direction or, more generally, the blade 22, 24 is deformed elastically, which is naturally reversible.

Because of the compressor air flowing in, the gas turbine compressor flow is also stabilized, which is especially important for the partial load range. Due to the air blown in, the pumping limit is shifted as far as possible to low throughputs.

The combination of the two compressor-stabilizing effects, namely the blown-in air and the adaptation of the blade geometry, makes an above average expansion of the stable operating range of a compressor possible. 

1-11. (canceled)
 12. A gas turbine, comprising: a blade, wherein the blade includes a phase-changeable shape-memory alloy and wherein the shape-memory alloy is a coating on the blade; and a channel, wherein the channel directs hot air and wherein the channel ends at the blade.
 13. The gas turbine according to claim 12, wherein the coating is on an outer side of the blade.
 14. The gas turbine according to claim 12, wherein the blade is a compressor blade.
 15. The gas turbine according to claim 12, wherein the channel starts from a downstream compressor stage and directs hot air upstream from the downstream compressor stage.
 16. The gas turbine according to claim 12, wherein the channel ends at a housing.
 17. The gas turbine according to claim 12, wherein the channel discharges into an interior of the blade and wherein hot air is blowable into the blade.
 18. The gas turbine according to claim 12, wherein the blade is a guide blade and/or a rotor blade.
 19. The gas turbine according to claim 12, wherein a variable guide baffle is not provided in the gas turbine.
 20. The gas turbine according to claim 12, wherein the blade is made of a metal alloy.
 21. A method for varying an aerodynamic shape of a blade of a gas turbine, comprising the steps of: conveying hot air on a shape-memory alloy coated on the blade; and causing a phase change of the shape-memory alloy by the conveyed hot air.
 22. The method according to claim 21, wherein the hot air is hot compressor air. 